*::after, *::before {
  box-sizing: border-box;
}

*{
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  display: flex;
  flex-flow: row wrap;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #29313a;
}

.input_box {
  position: relative;
  width: 350px;
}

.input_box input {
  position: relative;
  width: 100%;
  padding: 10px 0;
  background: transparent;
  border: none;
  outline: none;
  border-bottom: 2px solid #999;
  color: #FFF;
  font-size: 1.25em;
  letter-spacing: .05em;
  transform: .5s;
}

.input_box label {
  position: absolute;
  left: 0;
  padding: 10px 0;
  pointer-events: none;
  color: #666;
  user-select: none;
}

.input_box label span {
  position: relative;
  display: inline-block;
  flex-direction: row;
  font-size: 1.25em;
  letter-spacing: .05em;
  transition: .25s cubic-bezier(.5, 1, .5, 1.5);
}

.input_box input:focus ~ label span,
.input_box input:valid ~ label span {
  color: #0f0;
  text-shadow: 0 0 5px #0f0, 0 0 15px #0f0, 0 0 30px #0f0;
  transform: translateY(-30px);
}

.input_box input:focus,
.input_box input:valid {
  border-bottom: 2px solid #fff;
}